"These may not be the right criteria for identifying adults, who also may be quite impaired," he tells WebMD.

McGough is on a mission to have the criteria updated in the next edition of the Diagnostic and Statistical Manual of Mental Disorders (DSM), considered the bible of mental disorders. But it's not due out until 2012.

McGough is a professor clinical psychiatry at the UCLA Semel Institute for Neuroscience and Human Behavior. He lectured on adult ADHD at the annual meeting of the American Psychiatric Association.

Critique of ADHD Criteria

ADHD afflicts about 3% to 5% of school-age children; in 30% to 60% of them, the disorder will persist into adulthood. Overall, more than four in 100 U.S. adults have the disorder, according to McGough.

So what's wrong with the current criteria?

For starters, they state that patients should shows signs of hyperactivity, impulsivity, or inattentive behavior before age 7, he says.

"That's extremely impractical and not based on clinical evidence. Research suggests that the age of onset should be changed to age 16 or 18 years, or abandoned entirely," McGough says.

Also, many symptoms used to diagnose the disease don't apply to adults, he says. For example, one hallmark symptom is "running and climbing incessantly. For adults, better criteria might be frequently driving too fast or having trouble making appointments," he says.

Temple University's David Baron, DO, chairman of the committee that chose which studies to highlight at the meeting, says many adults -- and their doctors -- don't realize they have ADHD.

"Many other psychiatric disorders such as anxiety and depression come and go, but ADHD is more of a constant," he tells WebMD. "Because of that, people don't label it. Or they dismiss it. They say, 'Oh, I've been this way since the second grade.'"